var stream = require('stream');
var Readable = stream.Readable;

function MyReadable() {
    Readable.call(this);
}
MyReadable.prototype = Readable.prototype;

var rs = new MyReadable();

var c = 'a'.charCodeAt(0);

rs._read = function () {
    if (c <= 'z'.charCodeAt(0)) {
        rs.push(String.fromCharCode(c++));
    } else {
        rs.push(null);
    }
}
rs.pipe(process.stdout);